Optical displacement sensors are widely used in distance or displacement measurements. An exemplary distance measurement arrangement comprising an optical source, a position sensitive optical detector (PSD) and focus lens is shown in FIG. 1.
In such an optical arrangement, the distance of an object (L) from a reference point can be evaluated from the triangulation principle and is equal to Bf/x, where B is the baseline length between the optical axis of the optical source, which is an LED is the example, and the optical detector; f is the focal length; and x is of off-set distance from the central axis of the receiver lens.
A useful application of such an optical distance arrangement is in surface profiling of an object, for example, for liquid level monitoring, for surface profiling of a circuit or semiconductor assembly, for surface profiling of a mechanical mold, or other surface profile monitoring.
Optical displacement sensors for use in surface profiling or like applications are commonly available in a module form with an optical source and a PSD packaged within a module housing. To facilitate optimal optical performance a focusing lens is provided on the module housing for coupling optical output from the optical source to an external object and another focusing lens is provided on the module housing for collecting optical signals returned from the external object, for example, by reflection or scattering.
Examples of commercially available optical displacement sensor modules include Model AR600 of Acuity, Inc., Model GP2YOD340K of Sharp, Inc., and Model Nos. PZ-V11 and LK-G of Keyence, Inc.
An exemplary application of such optical displacement sensors for distance measurement is described in U.S. Pat. No. 6,879,407. Such an exemplary distance measurement arrangement typically comprises a movement mechanism for causing relative movements between the surface of an object to be scanned and the scanning optical displacement sensor. However, it is noted that such optical displacement sensors will give an erroneous output when an edge is encountered.
Therefore, it will be desirable if there can be provided improved optical displacement sensors and distance/displacement measuring apparatus incorporating same to alleviate shortcomings of conventional devices.